array.c

#include"stdlib.h"
#include"stddef.h"
#include"stdio.h"

typedef struct {
    int *arr;
    size_t len;
} Array;

Array iota(size_t len) {
    Array a;
    a.len = len;
    a.arr = (int*)malloc(sizeof(int) * len);
    for (int i = 0; i < len; i++) {
        a.arr[i] = i;
    }
    return a;
}

#define fail (-1)
size_t lin_search(Array a, int elem) {
    for (int i = 0; i < a.len; i++) {
        if (a.arr[i] == elem) return i;
    }
    return fail;
}


size_t bisect(Array a, int elem) {
    size_t hi = a.len - 1;
    size_t lo = 0;
    size_t mid;

    while (1) {
        mid = (hi + lo) >> 1;

        if (a.arr[mid] == elem) return mid;
        else if (a.arr[mid] > elem) hi = mid - 1;
        else lo = mid + 1;

        if (hi == lo) {
            return (a.arr[hi] == elem) ? hi : fail;
        }
    }
}

int main() {
    Array a = iota(20);

    printf("idx of 10: %d\n", lin_search(a, 10));
    printf("idx of 19: %llu", bisect(a, 19));
}